U.S. patent application number 12/299259 was filed with the patent office on 2009-03-19 for ranging regions for wireless communication relay stations.
This patent application is currently assigned to NORTEL NETWORKS LIMITED. Invention is credited to Jianglei Ma, Wen Tong, Hang Zhang, Peiying Zhu.
Application Number | 20090073916 12/299259 |
Document ID | / |
Family ID | 38801098 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090073916 |
Kind Code |
A1 |
Zhang; Hang ; et
al. |
March 19, 2009 |
RANGING REGIONS FOR WIRELESS COMMUNICATION RELAY STATIONS
Abstract
One embodiment of the present invention provides a unique
ranging technique in wireless communication environments that
employ relay stations associated with a base station. Each relay
station, and optionally the base station itself, can be allocated a
unique ranging region having unique ranging resources that may be
used by a mobile station to initiate a ranging function with the
corresponding relay station or base station.
Inventors: |
Zhang; Hang; (Nepean,
CA) ; Ma; Jianglei; (Kanata, CA) ; Zhu;
Peiying; (Kanata, CA) ; Tong; Wen; (Ottawa,
CA) |
Correspondence
Address: |
WITHROW & TERRANOVA, P.L.L.C.
100 REGENCY FOREST DRIVE, SUITE 160
CARY
NC
27518
US
|
Assignee: |
NORTEL NETWORKS LIMITED
St. Laurent
QC
|
Family ID: |
38801098 |
Appl. No.: |
12/299259 |
Filed: |
June 1, 2007 |
PCT Filed: |
June 1, 2007 |
PCT NO: |
PCT/IB07/01452 |
371 Date: |
October 31, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60810573 |
Jun 2, 2006 |
|
|
|
60892570 |
Mar 2, 2007 |
|
|
|
Current U.S.
Class: |
370/315 |
Current CPC
Class: |
H04B 7/15542 20130101;
H04W 92/10 20130101; H04W 88/04 20130101 |
Class at
Publication: |
370/315 |
International
Class: |
H04B 7/204 20060101
H04B007/204 |
Claims
1. A relay station to be associated with a base station and a
member relay station comprising: transmit and receive circuitry
adapted to facilitate wireless communications with the base station
and a mobile station; and a control system associated with the
transmit and receive circuitry and adapted to: identify a first
ranging region within an overall ranging region to use for a first
ranging function, wherein the member relay station uses a second
ranging region within the overall ranging region for the ranging
function; and detect a first ranging code transmitted by the mobile
station via first ranging resources within the first ranging
region; and process the first ranging code to facilitate the first
ranging function.
2. The relay station of claim 1 wherein in response to detecting
the ranging code, the control system is further adapted to: obtain
transmission adjustments for the mobile terminal to use when
transmitting information to the relay station; and send the
transmission adjustments to the mobile station.
3. The relay station of claim 2 wherein the control system is
further adapted to provide transmission adjustment recommendations,
which are used to determine the transmission adjustments for the
mobile terminal.
4. The relay station of claim 3 wherein to obtain the transmission
adjustments, the control system is further adapted to: determine
transmission adjustment recommendations; send code information
including or identifying the first ranging code and the
transmission adjustment recommendations to the base station; and
receive the transmission adjustments from the base station.
5. The relay station of claim 4 wherein the control system is
further adapted to send a mobile station identifier and information
identifying the first ranging resources or the first ranging region
along with the code information and the transmission adjustment
recommendations to the base station.
6. The relay station of claim 3 wherein the control system
determines the transmission adjustments based on the transmission
adjustment recommendations.
7. The relay station of claim 3 wherein the transmission adjustment
recommendations bear on one of a group consisting of transmission
time, transmission frequency, and transmission power associated
with transmission of the first ranging code.
8. The relay station of claim 1 wherein the base station uses a
third ranging region within the overall ranging region for the
first ranging function.
9. The relay station of claim 1 wherein the first and second
ranging regions have common ranging codes, including the first
ranging code, that can be assigned to the mobile station.
10. The relay station of claim 1 wherein the different ranging
codes are provided for each of the first and second ranging
regions.
11. The relay station of claim 1 wherein the wireless
communications with the mobile station are provided using
orthogonal frequency division multiplexing, the first ranging
region comprises a first group of sub-carriers within a transmit
frame, and the second ranging region comprises a second group of
sub-carriers within the transmit frame.
12. The relay station of claim 1 wherein ranging resources of the
first ranging region are orthogonal to ranging resources of the
second ranging region.
13. The relay station of claim 1 wherein the ranging function is an
initial ranging function provided prior to the mobile station
initiating data or voice communications via the relay station.
14. The relay station of claim 1 wherein the ranging function is a
periodic ranging function provided while the mobile station is
engaged in data or voice communications via the relay station.
15. The relay station of claim 1 wherein the ranging function is a
handoff ranging function provided while the mobile station is
engaged in a handoff procedure to transition from the relay station
to the member relay station.
16. The relay station of claim 1 wherein the ranging function is a
handoff ranging function provided while the mobile station is
engaged in requesting additional bandwidth from the relay
station.
17. The relay station of claim 1 wherein the control system is
further adapted to ignore ranging codes transmitted by the mobile
station via ranging resources of the second ranging region for the
ranging function.
18. The relay station of claim 1 wherein the control system is
further adapted to ignore ranging codes transmitted by the mobile
station via ranging resources outside of the first ranging region
for the first ranging function.
19. The relay station of claim 1 wherein to identify the first
ranging region, the control system is adapted to receive a message
from the base station, which allocates the first ranging region to
the first relay station and the second ranging region to the second
relay station.
20. A base station to be associated with a plurality of relay
stations capable of facilitating wireless communications with a
mobile station, the base station comprising: transmit and receive
circuitry adapted to facilitate wireless communications with the
plurality of relay stations and the mobile station; and a control
system associated with the transmit and receive circuitry and
adapted to: for each relay station of the plurality of relay
stations, identify a unique ranging region within an overall
ranging region to use for a first ranging function; receive a code
grab message from a first relay station of the plurality of relay
stations, the code grab message comprising transmission adjustment
recommendations and a first ranging code or an identifier of the
first ranging code that was received by the first relay station and
transmitted by the mobile station via first ranging resources
within a first ranging region of a plurality of ranging regions;
and process the first ranging code to facilitate the first ranging
function.
21. The base station of claim 20 further comprising sending a
message to each of the plurality of relay stations to allocate the
unique ranging region for each of the plurality of relay
stations.
22. The base station of claim 20 wherein to process the first
ranging code, the control system is further adapted to: determine
transmission adjustments for the mobile station to use when
transmitting information to the first relay station; and send the
transmission adjustments to the first relay station for delivery to
the mobile station.
23. The base station of claim 22 wherein the control system is
further adapted to: detect a second ranging code transmitted by the
mobile station via second ranging resources within a base station
ranging region; in response to detecting the second ranging code,
determine transmission adjustments for the mobile terminal to use
when transmitting information to the relay station; and send the
transmission adjustments to the mobile station.
24. The base station of claim 20 wherein the code grab message
further comprises a mobile station identifier and information
identifying the first ranging resources or the first ranging
region.
25. The base station of claim 20 wherein the control system is
further adapted to identify for the base station a unique base
station ranging region within an overall ranging region to use for
the first ranging function, such that each of the plurality of
relay stations and the base station are allocated different ranging
regions for the ranging function.
26. The base station of claim 25 wherein the control system is
further adapted to ignore ranging codes transmitted by the mobile
station via ranging resources outside of the unique base station
ranging region allocated for the base station.
27. The base station of claim 20 wherein the transmission
adjustment recommendations bear on one of a group consisting of
transmission time, transmission frequency, and transmission power
associated with transmission of the first ranging code.
28. The base station of claim 20 wherein ranging resources of each
of the plurality of ranging regions are orthogonal to one
another.
29. The base station of claim 20 wherein the ranging function is an
initial ranging function provided prior to the mobile station
initiating data or voice communications via one of the plurality of
relay stations.
30. The base station of claim 20 wherein the ranging function is a
periodic ranging function provided while the mobile station is
engaged in data or voice communications via the relay station.
31. The base station of claim 20 wherein the ranging function is a
handoff ranging function provided while the mobile station is
engaged in a handoff procedure to transition from one of the
plurality of relay stations to another of the plurality of relay
stations.
32. The base station of claim 20 wherein the ranging function is a
handoff ranging function provided while the mobile station is
engaged in requesting additional bandwidth from one of the
plurality of relay stations.
33. The base station of claim 20 wherein each of the plurality of
ranging regions have common ranging codes that can be assigned to
the mobile station.
34. The base station of claim 20 wherein the wireless
communications with the mobile station are provided using
orthogonal frequency division multiplexing, and each of the
plurality of ranging regions comprise unique groups of sub-carriers
within a transmit frame.
Description
[0001] This application is a 35 USC 371 national phase application
of PCT/IB2007/001452 filed Jun. 1, 2007, which claims priority to
U.S. provisional patent application Ser. No. 60/810,573 filed Jun.
2, 2006 and U.S. provisional patent application Ser. No. 60/892,510
filed Mar. 2, 2007, the disclosures of which are incorporated
herein by reference in their entireties.
FIELD OF THE INVENTION
[0002] The present invention relates to wireless communications,
and in particular to wireless communication systems that employ
relay stations.
BACKGROUND OF THE INVENTION
[0003] Wireless communication systems divide areas of coverage into
cells, each of which has traditionally been served by a base
station. The base stations support wireless communications with
mobile stations. The coverage area provided by a given base station
is generally referred to as a cell. As the mobile stations move
from one cell to another, the communication sessions are
transferred from one base station to another. Unfortunately, the
coverage area for a base station can be limited and may vary based
on geography and structures located within the coverage area.
[0004] In an effort to increase or improve the coverage area
provided by base stations, relay stations have been introduced.
Relay stations are associated with a given base station and act as
liaisons between the mobile stations within the coverage area of
the relay stations and the base station. For downlink
communications, data may be transmitted from the base station to a
relay station and from the relay station to the mobile station. For
uplink communications, data may be transmitted from the mobile
station to a relay station and from the relay station to the base
station. As such, the uplink or downlink path may have multiple
hops. Further, multiple relay stations may be provided in the
uplink or downlink path. Even when relay stations are employed,
mobile stations and base stations may also communicate directly, if
the mobile stations are within communication range of the base
stations.
[0005] As the demand for high speed broadband networking over
wireless communication networks increases, so too does the demand
for different types of networks that can accommodate high speed
wireless networking. For example, the deployment of IEEE
802.11-based wireless networks in homes and business to create
Internet access "hot spots" has become prevalent in today's
society. However, these IEEE 802.11-based wireless networks are
relatively limited in bandwidth as well as communication distance.
Thus, these IEEE 802.11-based wireless networks are not good
candidates for cellular implementations to provide continuous
coverage over extended areas.
[0006] In an effort to increase bandwidth and communication
distance for longer range wireless networking, the family of IEEE
802.16 standards was developed for next generation wireless
communications systems that are cellular based. The IEEE 802.16
standards are often referred to as WiMAX, and provide a
specification for fixed broadband wireless metropolitan access
networks (MANs) that use a point-to-multipoint architecture. Such
communications can be implemented, for example, using orthogonal
frequency division multiplexing (OFDM) communication. OFDM
communication uses a spread spectrum technique to distribute the
data over a large number of carriers that are spaced apart at
precise frequencies.
[0007] The IEEE 802.16 standards support high bit rates in both
uplink and downlink communications up to a distance of about 30
miles (.about.50 km) to handle such services as Voice over Internet
Protocol (VoIP), IP connectivity and other voice, media, and data
applications. Expected data throughput for a typical WiMAX network
is 45 MBits/sec. per channel. IEEE 802.16 networks, such as IEEE
802.16j, networks, can be deployed as multi-hop networks, which
employ relay stations to act as liaisons between base stations and
mobile stations and further extend the effective coverage areas of
the associated base stations.
[0008] For multi-hop networks, including those employing the IEEE
802.16 standards, there is a need for efficient and effective
techniques to provide various ranging functions, channel quality
reporting functions, and retransmission control functions when the
mobile stations are being served by relay stations. These functions
are often critical to enabling effective communications. For
example, initial and periodic ranging functions help ensure that
mobile stations transmit at the appropriate time and power on the
right frequency. The channel quality reporting function helps a
mobile station identify and select an appropriate base station or
relay station with which to anchor while the retransmission control
function ensures that lost data is retransmitted as necessary.
Currently, these functions are controlled primarily by the base
station that is associated with the relay stations, and the
resources of the group are often used inefficiently and performance
is degraded.
SUMMARY OF THE INVENTION
[0009] One embodiment of the present invention provides a unique
ranging technique in wireless communication environments that
employ relay stations, which are associated with a base station.
Each relay station, and perhaps the base station itself, is
allocated a unique ranging region. Each ranging region has unique
ranging resources that may be used by a mobile station to initiate
a ranging function with the corresponding relay station or base
station. The mobile station may select a relay station for ranging
and then select ranging resources from the ranging region allocated
to the selected relay station.
[0010] A ranging code is then transmitted by the mobile station
using the ranging resources for the ranging region allocated to the
selected relay station. The selected relay station will monitor the
ranging resources assigned to it and detect the ranging code that
was transmitted from the mobile station. The relay station will
take steps to obtain transmission adjustments for the mobile
station in light of receiving the ranging code, and will send
transmission adjustments to the mobile station. The relay station
may send transmission adjustment recommendations with the ranging
code or information identifying the ranging code to the base
station, which will determine actual transmission adjustments based
on the transmission adjustment recommendations. Alternatively, the
relay station may determine the transmission adjustments without
employing the base station.
[0011] The ranging functions may provide initial or periodic
ranging functions. Mobile terminals generally use the transmission
adjustments from these ranging functions to control the timing,
frequency, or power for subsequent transmissions. An initial
ranging function is provided prior to initiating primary
communications via the relay station or directly with the base
station. A periodic ranging function is provided during the primary
communications via the relay station or directly with the base
station.
[0012] Those skilled in the art will appreciate the scope of the
present invention and realize additional aspects thereof after
reading the following detailed description of the preferred
embodiments in association with the accompanying drawing
figures.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0013] The accompanying drawing figures incorporated in and forming
a part of this specification illustrate several aspects of the
invention, and together with the description serve to explain the
principles of the invention.
[0014] FIG. 1 is a wireless communication environment according to
one embodiment of the present invention.
[0015] FIG. 2 illustrates common ranging regions in select frames
according to one embodiment of the present invention.
[0016] FIG. 3 is communication flow diagram illustrating a common
ranging process according to one embodiment of the present
invention.
[0017] FIG. 4 illustrates distributed ranging regions in select
frames according to one embodiment of the present invention.
[0018] FIG. 5 is communication flow diagram illustrating a
distributed ranging process according to one embodiment of the
present invention.
[0019] FIG. 6 is communication flow diagram illustrating a periodic
ranging process according to one embodiment of the present
invention.
[0020] FIG. 7 is communication flow diagram illustrating an
intra-cell fast switching process employing a synchronized channel
quality indicator channel according to one embodiment of the
present invention.
[0021] FIG. 8 is communication flow diagram illustrating an
intra-cell fast switching process employing a non-synchronized
channel quality indicator channel according to one embodiment of
the present invention.
[0022] FIG. 9 is a wireless communication environment where a
diversity controller is provided in the base station according to
one embodiment of the present invention.
[0023] FIG. 10 is a wireless communication environment where a
diversity controller is provided in a relay station apart from the
relay station that is anchoring the mobile station according to one
embodiment of the present invention.
[0024] FIG. 11 is communication flow diagram illustrating
macro-diversity for downlink communications according to one
embodiment of the present invention.
[0025] FIG. 12 is communication flow diagram illustrating
macro-diversity for uplink communications according to one
embodiment of the present invention.
[0026] FIG. 13 is a protocol stack according to one embodiment of
the present invention.
[0027] FIGS. 14A and 14B are a communication flow diagram
illustrating a first retransmission control process according to
one embodiment of the present invention.
[0028] FIGS. 15A and 15B are a communication flow diagram
illustrating a second retransmission control process according to
one embodiment of the present invention.
[0029] FIG. 16 is a block representation of a base station
according to one embodiment of the present invention.
[0030] FIG. 17 is a block representation of a mobile terminal
according to one embodiment of the present invention.
[0031] FIG. 18 is a block representation of a relay station
terminal according to one embodiment of the present invention.
[0032] FIG. 19 is a logical breakdown of an OFDM transmitter
architecture according to one embodiment of the present
invention.
[0033] FIG. 20 is a logical breakdown of an OFDM receiver
architecture according to one embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] The embodiments set forth below represent the necessary
information to enable those skilled in the art to practice the
invention and illustrate the best mode of practicing the invention.
Upon reading the following description in light of the accompanying
drawing figures, those skilled in the art will understand the
concepts of the invention and will recognize applications of these
concepts not particularly addressed herein. It should be understood
that these concepts and applications fall within the scope of the
disclosure and the accompanying claims.
[0035] The present invention provides various techniques for
improving wireless communications in wireless communication
environments that employ relay stations. In general, relay stations
are employed to extend the coverage area of a given base station by
allowing the base station to communicate with a given mobile
terminal via the relay station. With reference to FIG. 1, an
exemplary communication environment 10 is illustrated, wherein a
basic carrier network 12 supports multiple base stations (BS) 14.
In general, the base stations 14 are capable of facilitating
wireless communications with any mobile station 16 that is within
an available communication range. Of the three base stations 14
illustrated in FIG. 1, BS1, BS2, and BS3, base station BS2 is
associated with numerous relay stations 18, RS1-RSN. Given the
location of the mobile station 16, the mobile station 16 may
facilitate communications directly with the base station BS2 or
indirectly with the base station BS2 through relay stations RS1 and
RS2. Notably, the mobile station 16 may be located in an area that
inhibits, and possibly even prohibits, direct communications with a
base station 14, and as such, communications may be passed through
a relay station 18 that is within communication range of the mobile
station 16.
[0036] In most wireless communication environments, extensive
efforts are made to minimize the interference that any given
communication session has on other communication sessions within
the same area. These efforts to minimize interference generally
include controlling when different entities communicate, the
channel to use when communicating, and the power to use to
facilitate the communications. Accordingly, the mobile station 16,
base station 14, and relay stations 18 cooperate to ensure that
uplink (UL) communications from different mobile stations 16 arrive
at the relay stations 18 or base stations 14 in a synchronized
fashion and at relatively the same power levels. Synchronization of
these communications generally requires that communications by the
mobile station 16 be synchronized in time, and often in frequency,
because the frequency used for communications defines all or part
of the channel used to facilitate the communications.
[0037] To facilitate such synchronization, initial ranging
techniques are employed to adjust the timing, frequency, and power
that are used by the mobile station 16 to facilitate
communications. Each mobile station 16 will participate in initial
ranging prior to initiating communications. Once communications
have commenced, periodic ranging may be employed to provide
periodic adjustments to the timing, frequency, and power that are
used by the mobile station 16 to facilitate ongoing communications.
For initial or periodic ranging, the mobile station 16 will
transmit an appropriate ranging code that is received by a relay
station 18 or a base station 14, which will process the ranging
code and communication parameters associated with actually
receiving the ranging code to determine adjustments in timing,
frequency, or power for the mobile station 16 to use for subsequent
communications.
[0038] A ranging code is transmitted using defined communication
resources, which for OFDM may be a defined group of sub-carriers
along a time-frequency continuum that defines a transmission frame.
The resources allocated for transmitting ranging codes are
generally referred to as a ranging region. Each ranging region may
include different sets of ranging resources that may be used at the
same time by multiple mobile stations 16, or may be divided and
distributed among multiple mobile stations 16, such that different
mobile stations 16 have unique ranging resources within a given
geographic area.
[0039] In one embodiment, a common initial ranging region is
provided for multiple mobile stations 16 to use. Accordingly,
different mobile stations 16 may use the ranging resources within a
common ranging region at the same time within a given geographic
area. Preferably, different ranging code sets are assigned to
different ones of the relay stations 18 and base stations 14. A
ranging code within the code set is selected by each mobile station
16 and transmitted using the ranging resources within the common
ranging region. Thus, the mobile station 16 can alert the relay
stations 18 and the base stations 14 as to its intention of
communicating with a particular one of the relay stations 18 or
base stations 14 based on the code set from which the ranging code
was selected. FIG. 2 illustrates a scenario where uplink frames
intended for relay stations RS1 and RS2, along with base station
BS2, have common ranging regions within which different mobile
stations 16 may simultaneously transmit ranging codes.
[0040] With reference to the communication flow diagram of FIG. 3,
an exemplary common initial ranging process is described.
Initially, a mobile station 16 will start an initial ranging
process (step 100) by selecting an initial ranging code (IRC) from
a code set that is uniquely associated with one of the relay
stations RS1, RS2, and the base station BS2 (step 102). In this
case, assume the mobile station 16 is associated with relay station
RS1, but is within communication range of relay station RS2 and
base station BS2. Once the initial ranging code is selected, the
mobile station 16 will transmit the initial ranging code (step
104). Notably, the initial ranging code transmitted by the mobile
station 16 may be received by the relay station RS1, the relay
station RS2, and the base station BS2, even through the mobile
station 16 intends for the IRC to be received by relay station
RS1.
[0041] Each of the relay station RS1, relay station RS2, and base
station BS2 will detect the initial ranging code and determine
transmission (TX) adjustment recommendations in light of reception
characteristics associated with actually receiving and decoding the
initial ranging code (steps 106, 108, and 110). The transmission
adjustment recommendations may relate to any synchronization
parameters, such as timing, frequency, and power associated with
uplink communications from the mobile station 16 to one of the
relay station RS1, relay station RS2, and base station BS2. The
relay stations RS1 and RS2 will send code grab messages to the base
station BS2, wherein the code grab messages may include a code
index corresponding to the initial ranging code that was received,
an opportunity index identifying the ranging resources within the
common ranging regions that were used for transmitting the initial
ranging code, the mobile station's ID (MSID) if available, and the
transmission adjustment recommendations (steps 112 and 114).
[0042] Next, the base station BS2 will process the code grab
messages and select one of the relay stations RS1 and RS2, or
itself, to use for sending transmission adjustments back to the
mobile station 16 (step 116). Selection of one of the relay
stations RS1 and RS2 or the base station BS2 to use for providing
the transmission adjustments is generally based on the transmission
adjustment recommendations determined by the base station BS2 or
received from the relay stations RS1 and RS2. The actual
transmission adjustments to provide to the mobile station 16 are
selected from the transmission adjustment recommendations for the
selected one of the relay stations RS1 and RS2 and the base station
BS2. At this point, the base station BS2 will send transmission
adjustments to the mobile station 16, directly or via the selected
relay station RS1 or RS2. In this example, assume the base station
BS2 selected relay station RS2 to provide the transmission
adjustments to the mobile station 16. As such, the base station BS2
will send a code grab response with transmission adjustments to the
relay station RS2 (step 118), which will send a ranging response
with the transmission adjustments to the mobile station 16 (step
120).
[0043] In one embodiment of the present invention, different
coordinated ranging regions are provided for associated relay
stations 18 and base stations 14. As illustrated in FIG. 4, a
different ranging region within an uplink frame is allocated to
relay station RS1, relay station RS2, and base station BS2. As
such, different ranging resources are used with different relay
stations 18 or base stations 14. Thus, each base station 14 and
relay station 18 associated with the base station 14 has a unique
ranging region, which may be determined and allocated by the base
station 14. Preferably, the ranging regions of neighboring relay
stations 18 and associated base station 14 are orthogonal, in that
the resources for the different ranging regions have different
time-frequency locations within the uplink frame. If the relay
stations 18 and associated base station 14 are far enough apart
where interference is not an issue, certain relay stations 18 or
base stations 14 may have common ranging regions. These ranging
regions may be used for initial ranging, periodic ranging,
bandwidth request ranging, and handover ranging. Bandwidth request
ranging is simply ranging where requests for more or less bandwidth
are being made, whereas handover ranging is ranging in preparation
for a handoff from one relay station 18 to another, or from a relay
station 18 to a base station 14. Accordingly, the ranging region in
which a ranging code is transmitted will indicate the particular
relay station 18 or base station 14 to which transmission of the
ranging code was intended. In other words, the mobile station 16
can indicate its selection of a particular relay station 18 or base
station 14 based on the ranging region selected for transmitting
the ranging code.
[0044] Turning to the communication flow of FIG. 5, a coordinated
initial ranging process is described according to one embodiment of
the present invention. Initially, base station BS2, which is
associated with relay stations RS1 and RS2, will identify initial
ranging regions for each of the relay stations RS1 and RS2 (step
200). The different initial ranging regions are assigned to the
respective relay stations RS1 and RS2 (steps 202 and 204), wherein
each relay station RS1 and RS2 is aware of its unique initial
ranging region. Notably, the base station BS2 may also determine a
unique initial ranging region for itself.
[0045] Assuming the mobile station 16 is aware of the initial
ranging regions assigned to the relay stations RS1 and RS2 and the
base station BS2, the mobile station 16 will start initial ranging
(step 206) by selecting a relay station 18 (or base station 14)
based on various downlink parameters (step 208). The downlink
parameters may be various transmissions, such as pilot symbol
transmissions, from the relay stations RS1 and RS2 and the base
station BS2. Assuming the mobile station 16 selects relay station
RS1 for initial ranging, the mobile station 16 will select a
ranging resource from the initial ranging region of the selected
relay station RS1 (step 210). An initial ranging code is then
selected (step 212) and transmitted by the mobile station 16 (step
214). Notably, the initial ranging code is sent via the ranging
resource of the initial ranging region, which was allocated to
relay station RS1. The initial ranging code transmitted by the
mobile station 16 will not be processed by relay station RS2 or
base station BS2, because the initial ranging code was not
transmitted using ranging resources within the initial ranging
regions associated with relay station RS2 or base station BS2.
Accordingly, only relay station RS1 will detect the initial ranging
code and determine transmission adjustment recommendations that
bear on the time, frequency, or power used to transmit the initial
ranging code (step 216).
[0046] The relay station RS1 may send to the base station BS2 a
code grab message identifying a code index associated with the
initial ranging code, an opportunity index identifying the
resources used for transmitting the initial ranging code, the MSID
of the mobile station 16 if available, and the transmission
adjustment recommendations (step 218). The base station BS2 will
determine transmission adjustments for the mobile station 16 based
on the transmission adjustment recommendations (step 220). The base
station BS2 will then send a code grab response including the
transmission adjustments to the relay station RS1 (step 222), which
will send the transmission adjustments in a ranging response
message to the mobile station 16 (step 224). Although the above
example is described in association with initial ranging, handoff,
periodic, and bandwidth request ranging may take advantage of these
techniques.
[0047] When mobile stations 16 can communicate with multiple relay
stations 18 or base stations 14, fast switching and macro diversity
handoff techniques may be employed. Fast switching techniques allow
a given mobile station 16 to rapidly switch from one relay station
18 or base station 14 to another based on channel conditions,
resource availability, and the like. In general, although the
mobile station 16 can communicate with multiple ones of the relay
stations 18 and base stations 14 at a given time, only one relay
station 18 or base station 14 is communicated with at any given
time. In contrast, macro diversity handoff, which is often referred
to as a soft handoff, allows a mobile station 16 to simultaneously
communicate with two or more relay stations 18 and base stations 14
at the same time. Macro diversity handoff may support uplink and
downlink communications. Accordingly, two or more relay stations 18
and base stations 14 may receive a transmission from a mobile
station 16, and may cooperate to either select or combine the
received information. Similarly, a mobile station 16 may receive
the same information from two or more of the relay stations 18 or
base stations 14 and may use selection or combining techniques to
recover the transmitted information. For fast switching or macro
diversity handoffs, it is important for the participating relay
stations 18 and base stations 14 to have up-to-date ranging
information, such that uplink or downlink communications between
the mobile station 16 and one of the relay stations 18 or base
stations 14 are properly received and synchronized with
transmissions from other mobile stations 16.
[0048] Prior to the present invention, a separate association
process was required for each participating relay station 18 and
base station 14. During the association process, an initial ranging
procedure had to take place prior to initiating communications.
This association process has proven to be time-consuming and
inefficient. In one embodiment of the present invention, a common
periodic ranging process is employed to avoid the need for an
association process for fast switching and macro diversity handoff
scenarios. In essence, a periodic ranging process is provided by an
anchoring relay station 18 or base station 14. The anchoring relay
station 18 or base station 14 will then share the ranging resources
with other participating relay stations 18 and base stations 14.
Thus, relay stations 18 and base stations 14 that are not anchoring
communications with the mobile station 16 have ranging information
without employing any separate association procedure.
[0049] With reference to FIG. 6, an exemplary periodic ranging
procedure is provided according to one embodiment of the present
invention. The mobile station 16 will start periodic ranging (step
300) by transmitting a periodic ranging code (PRC) (step 302).
Assume that the periodic ranging process employs a common periodic
ranging region, wherein each of the relay stations RS1 and RS2 and
the base station BS2 share the ranging resources within the common
periodic ranging region. In this embodiment, assume that a
different periodic ranging code set of multiple periodic ranging
codes is allocated for each of the relay stations RS1 and RS2 as
well as for the base station BS2. Further assume that relay station
RS1 is an anchor for communications with the mobile station 16, and
that the periodic ranging code transmitted by the mobile station 16
is one that was selected from the periodic ranging code set
assigned to the relay station RS1.
[0050] Once transmitted, the periodic ranging code is received by
relay station RS1, relay station RS2, and base station BS2, which
will detect the periodic ranging code and the code parameters
associated with receiving the periodic ranging code (steps 304,
306, and 308). In this embodiment, relay station RS1 is able to
identify the mobile station 16 that transmitted the periodic
ranging code; however, the relay station RS2 and the base station
BS2 are not able to identify the mobile station 16 that transmitted
the periodic ranging code. The relay station RS1 is able to
identify the mobile station 16 that transmitted the periodic
ranging code because the relay station RS1 previously assigned that
particular code to the mobile station 16, or previously scheduled
transmission of the periodic ranging code by the mobile station 16.
Accordingly, the relay station RS1 will identify the mobile station
16 that sent the periodic ranging code (step 310) and then
determine transmission adjustments to apply for subsequent
communications (step 312). The transmission adjustments are sent in
a ranging response to the mobile station 16 (step 314), which will
make the transmission adjustments and facilitate uplink
communications accordingly.
[0051] Since the relay station RS2 and the base station BS2 are not
able to identify the mobile station 16 that transmitted the
periodic ranging code, the relay station RS1 will send an update
message including a code index for the periodic ranging code, an
opportunity index identifying the resources used to transmit the
periodic ranging code, and the MSID of the mobile station 16 to the
base station BS2 (step 316). The base station BS2 will update its
ranging information for the mobile station 16 based on information
provided by the relay station RS1 (step 318). The base station BS2
will then send a similar update including the code index,
opportunity index, and MSID that is associated with the periodic
ranging code received at relay station RS1 to relay station RS2
(step 320). Relay station RS2 will update its ranging information
for the mobile station 16 (step 322). The relay station RS2 and
base station BS2 will now be able to identify the mobile station 16
that is associated with transmitting the periodic ranging codes,
and will be better prepared to participate in fast switching and
macro diversity handoff scenarios.
[0052] In many fast switching scenarios, the mobile station 16
analyzes channel conditions associated with downlink communications
from different relay stations 18 or base stations 14, and
determines whether to switch from one to another based on the
channel conditions. Although base stations 14 can participate in
fast switching with associated relay stations 18, the following
discussion focuses on fast switching between two relay stations RS1
and RS2 for clarity and conciseness. In general, a channel quality
indication (CQI) is determined by the mobile station 16 and
transmitted over a previously allocated CQI channel. The CQI
channel is generally allocated to the mobile station 16 by the
relay station 18 (or base station 14) that is currently anchoring
communications with the mobile station 16. The participating relay
stations 18 and base stations 14 that are associated with the
anchoring relay station 18 (or base station 14) are called member
stations.
[0053] In one embodiment, the CQI assignment is synchronized among
the participating relay stations 18 and base stations 14. The
process is best illustrated in association with the communication
flow of FIG. 7. Initially, assume an anchoring relay station RS1
selects a CQI channel for use by the mobile station 16 (step 400)
and transmits a CQI channel allocation identifying the selected CQI
channel to the mobile station 16 (step 402). To synchronize the CQI
channel assignment, the anchoring relay station RS1 will send a CQI
channel update identifying the CQI channel allocated for the mobile
station 16 and the MSID of the mobile station 16 to the base
station 14 (step 404). The base station BS2 will send a similar CQI
channel update to the relay station RS2 (step 406). The relay
station RS2 will make note of the CQI channel being used by the
mobile station 16 and provide a CQI channel update response to
confirm receipt of the CQI channel information to the base station
BS2 (step 408). The base station BS2 will also send a CQI channel
update response to the anchoring relay station RS1 to indicate that
the CQI channel information has been provided to the relay station
RS2 (step 410).
[0054] During this time, the mobile station 16 will monitor the
channel quality of the link between the mobile station 16 and the
anchoring relay station RS1, and will transmit a corresponding
channel quality indicator via the allocated CQI channel (step 412).
The channel quality indicator may be received and monitored by the
anchoring relay station RS1 as well as the relay station RS2. The
mobile station 16 will also monitor the channel quality associated
with the relay station RS2. The mobile station 16 will monitor the
channel quality of the links with the anchor relay station RS1 and
the relay station RS2, and at some point, the channel quality
associated with the link with relay station RS2 will become better
than that of the link associated with the anchor relay station RS1.
At this point, the mobile station 16 may decide to switch
communications from the anchor relay station RS1 to the relay
station RS2 (step 414). Accordingly, the mobile station 16 will
send a switching request via the allocated CQI channel to indicate
the desire to switch communications from the anchoring relay
station RS1 to relay station RS2 (step 416). The switching request
may be received by the anchoring relay station RS1 and relay
station RS2, and in response, the anchoring relay station RS1 and
relay station RS2 will send switching alert messages indicating the
desire of the mobile station 16 to switch from the anchoring relay
station RS1 to relay station RS2 (steps 418 and 420). Notably, the
switching alert message will identify at least the relay station
RS2 to which communications are to be switched, and the MSID of the
mobile station 16.
[0055] The base station BS2 may determine whether to prevent the
mobile station 16 from switching communications from the anchoring
relay station RS1 to relay station RS2 (step 422). If the base
station BS2 does not intervene to prevent switching, the anchoring
relay station RS1 will send a switching response to indicate that
switching from the anchoring relay station RS1 to relay station RS2
is authorized (step 424). At this point, the mobile station 16 and
the relay station RS2 begin supporting communications, and thus the
relay station RS2 becomes the anchoring relay station (step 426).
Once communications are established with relay station RS2, relay
station RS2 may send a message indicating that the switch has been
completed to the base station BS2 (step 428). With this embodiment,
the targeted (relay or base) station to which communications are
being switched is notified of the desire to switch by the mobile
station 16 as the currently anchoring (relay or base) station.
[0056] With reference to FIG. 8, a communication flow is
illustrated wherein the CQI channel is not synchronized. Initially,
an anchoring relay station RS1 selects a CQI channel for use by the
mobile station 16 (step 500). The CQI channel is assigned to the
mobile station 16 via a CQI channel allocation message (step 502),
wherein the mobile station 16 will provide channel quality
indicators via the CQI channel to the anchoring relay station RS1
(step 504). As above, the mobile station 16 will monitor channel
quality associated with links with the anchoring relay station RS1
and the relay station RS2, and at some point will decide to switch
communications from the anchoring relay station RS1 to relay
station RS2 (step 506). The mobile station 16 will send a switching
request via the CQI channel to the anchoring relay station RS1
(step 508). The anchoring relay station RS1 will send a switching
request alert identifying the targeted relay station RS2 and the
mobile station 16 to the base station BS2 (step 510). The base
station BS2 will send a switching alert to the targeted relay
station RS2 and identify the mobile station 16 using the MSID for
the mobile station 16 (step 512). The targeted relay station RS2
will select a CQI channel for the mobile station 16 to use when
reporting channel quality to the targeted relay station RS2 (step
514). The relay station RS2 will then send a switching alert
response back to the base station BS2, wherein the switching alert
response including the selected CQI channel and the MSID for the
mobile station 16 (step 516). In response, the base station BS2
will send a switching alert response message to the currently
anchoring relay station RS1 (step 518). Again, the switching alert
response message will include the CQI channel for the mobile
station 16 to use for providing CQI to the targeted relay station
RS2. The anchoring relay station RS1 will send a switching request
response including the new CQI channel to the mobile station 16
(step 520). At this point, the mobile station 16 will provide a CQI
for the channel quality associated with the link with relay station
RS2 via the new CQI channel (step 522). During this time, the
mobile station 16 will switch communications from the relay station
RS1 to the relay station RS2, which is not the anchoring relay
station for communications (step 524). The relay station RS2 may
send a switch complete message to the base station BS2 to indicate
that communications have been switched from relay station RS1 to
relay station RS2 (step 526). From the above, CQI channel
allocation may be employed to enhance fast switching techniques
among associated relay stations 18 and base stations 14.
[0057] Macro diversity may take on various configurations depending
on the location of the relay stations 18 relative to the associated
base station 14 and the mobile station 16 being served. With
reference to FIG. 9, uplink or downlink macro diversity may be
provided between relay station RS1 and relay station RS2, as well
as with base station 14. Uplink or downlink communications
associated with the relay station RS1 are relayed between the relay
station RS1 and the base station 14. Similarly, communications
between relay station RS2 and the mobile station 16 are relayed
between the relay station RS2 and the base station 14. As noted,
uplink and downlink communications may be supported directly by the
base station 14 as well. For downlink communications, the base
station 14 will send the same data to be transmitted to the mobile
station 16 to the relay station RS1 and the relay station RS2, and
at a certain time on a given channel, the relay station RS1, relay
station RS2, and base station 14 may transmit the same information
to the mobile station 16, which will receive the downlink
transmission and combine them to recover the transmitted
information. The relay or base stations 18, 14 participating in
macro diversity for a given mobile station 16 define a macro
diversity set. Generally, the anchoring station, which is
illustrated as being relay station RS1, will provide a diversity
control function. With the present invention, the diversity control
function is provided in a diversity controller (DC) 19, which need
not be in the relay or base station 18, 14 that is the anchor
station. As illustrated in FIG. 9, the diversity controller 19 is
provided in the base station 14, even though relay station RS1 acts
as an anchor station for the mobile station 16. Thus, the primary
link for communications is between relay station RS1 and the mobile
station 16; however, the mobile station 16 may combine
transmissions from the relay station RS1, the relay station RS2,
and the base station 14. Similarly, transmissions from the mobile
station 16 may be received by the relay station RS1 and relay
station RS2, and forwarded to the base station 14, wherein the base
station 14 will combine the transmissions received via the relay
stations RS1 and RS2 as well as those received directly at the base
station 14 to recover the transmitted information. Notably, the
initial and periodic ranging techniques described above can be used
to identify the participating relay stations 18 and base stations
14, in a macro diversity (or handoff) set.
[0058] Preferably, the diversity controller 19 is provided in the
base station 14 for the macro diversity set, or the relay station
18 that is closest to the base station 14 in the macro diversity
set, as illustrated in FIGS. 9 and 10, respectively. In FIG. 10,
the relay station RS2 can actually transmit information intended
for the mobile station 16 via relay station RS1, which as
illustrated, acts as an anchor station for the mobile station 16.
For uplink macro diversity, transmissions from the mobile station
16 are received by relay station RS1 and relay station RS2. Relay
station RS1 will forward the received information to relay station
RS2, which will combine the information to recover the transmitted
information, and then provide the transmitted information to the
base station 14. For downlink communications, the diversity
controller 19 of the relay station RS2 may send information to be
transmitted to the mobile station 16 to the relay station RS1, and
at a defined time and over an appropriate channel, both the relay
station RS2 and the relay station RS1 will transmit information to
the mobile station 16. Thus, the diversity controller 19 is
responsible for multicasting downlink communications to any
downstream relay stations 18 and to the mobile station 16, as well
as combining direct transmissions for uplink communications. Again,
the diversity controller 19 is preferably provided in the base
station 14 itself or in the relay station 18 that is closest to the
base station 14 of the macro diversity set, regardless of the
anchoring relay or base station. Further, the relay station 18 or
base station 14 that provides the diversity controller 19 may
control the scheduling of uplink and downlink communications for
the mobile station 16. As the mobile station 16 moves, the
diversity controller 19 allocated to the mobile station 16 may move
from station to station.
[0059] The base station 14 may always provide the diversity
controller 19. However, if the diversity controller 19 is not in
the base station 14, the diversity controller 19 may be provided in
the anchor relay station 18, which may be employed to schedule
uplink and downlink transmissions. Alternately, the anchor relay
station 18 may schedule transmissions and then inform the diversity
controller 19, which may be located in the same or in a different
relay station 18. In general, the anchor station is the station
from which the mobile station 16 receives the strongest downlink
signal.
[0060] With reference to FIG. 11, a communication flow is provided
to illustrated downlink communications in a macro diversity
scenario for the communication environment of FIG. 9. Initially,
assume the diversity controller 19 is located in the base station
14, and relay station RS1 is an anchor station for the mobile
station 16. The diversity controller 19 of the base station 14 will
multicast data intended for the mobile station 16 to the relay
stations RS1 and RS2 (step 600). The multicast may also include
information identifying a resource allocation for the downlink
communications, and as such, the relay stations RS1 and RS2 will be
informed of the resources to use when transmitting the data to the
mobile station 16. The diversity controller 19 of the base station
14 may also send a downlink (DL) map, which identifies the downlink
resources that will be used for transmissions to the mobile station
16 by the relay stations RS1 and RS2, and perhaps the base station
14 (step 602). At the appropriate time and using the appropriate
channel in light of any transmission adjustments from prior ranging
operations, relay station RS1, relay station RS2, and the base
station 14 may transmit the same data to the mobile station 16
(steps 604A, 604B, and 604C). the mobile station 16 will receive
these transmissions at substantially the same time and combine the
transmissions from relay station RS1, relay station RS2, and the
base station 14 to recover the transmitted information (step
606).
[0061] With reference to FIG. 12, an uplink communication scenario
is illustrated for the macro diversity of FIG. 9. Again, the
diversity controller 19 is provided in the base station 14, and
relay station RS1 is an anchor station for the mobile station 16.
Initially, the base station 14 will provide uplink resource
allocations for the transmissions for the mobile station 16 to the
relay stations RS1 and RS2 (step 700). The base station 14 will
also send an uplink (UL) map message identifying the uplink
resources that will be used by relay stations RS1 and RS2, and
perhaps the base station 14 to the mobile station 16 (step 702).
The mobile station 16 will then transmit data at the allocated time
and over the allocated channel (step 704). The transmitted data may
be received by the relay station RS1, relay station RS2, and the
base station 14. Accordingly, the relay station RS1 will forward
the data received from the mobile station 16 to the base station 14
(step 706A). The relay station RS2 will send the data it received
from the mobile station 16 to the base station 14 (step 706B). At
this point, the base station 14 will combine the data from the
transmissions received from relay stations RS1 and RS2, as well as
directly at the base station 14 to recover the information
transmitted by the mobile station 16 (step 708).
[0062] Another embodiment of the present invention relates to
implementation of an improved error control technique. In
particular, an automatic repeat request (ARQ) mechanism and a
hybrid ARQ mechanism cooperate to provide efficient retransmission
of data. In general, ARQ is an error control method for data
transmission systems, and employs acknowledgement messages and
timeout mechanisms to ensure that all data that is transmitted is
properly received. Typically, an acknowledgement message is sent by
a receiver to the transmitter to indicate that each data packet is
correctly received. Generally, when the transmitter does not
receive an acknowledgement before a timeout occurs, the transmitter
will retransmit the frame. The receiver may send a negative
acknowledgement if it is determined that a packet is not properly
received, or is lost. Hybrid ARQ is a variant of ARQ, and generally
employs some type of coding within each data packet to indicate
whether or not the data packets were properly received. For
example, each packet may be encoded with an error correction code.
As the packets are received, they are analyzed in light of the
error correction code to determine whether or not each of the
packets was received. If a packet must be retransmitted, the
receiver may request retransmission of the packet.
[0063] In a communication environment employing relay stations 18,
multiple hops are required to reach a mobile station 16 from a base
station 14. Generally, the hops from a base station 14 to a relay
station 18 and between relay stations 18 are relatively reliable.
The least reliable hop is between the last relay station 18 in the
path and the mobile station 16. In many instances, the probability
of a failed transmission attempt is very high in this last hop due
to the changing channel conditions associated with the mobility of
the mobile station 16. When employing basic ARQ techniques when
relay stations 18 are employed, the base station 14 must re-send
data through the relay stations 18 to the mobile station 16, even
though the only failed link is between the last relay station 18
and the mobile station 16. Thus, significant resources are wasted
by retransmitting the packets from the base station 14 to the last
relay station 18 in the forwarding path.
[0064] For the present invention, ARQ is employed at a MAC, or
layer 2, level, while hybrid ARQ is employed at a physical, or
layer 1, level. Further, ARQ is performed on an end-to-end basis
across multiple links between entities, wherein hybrid ARQ is
performed on a per-link basis. With reference to FIG. 13, an
exemplary protocol stack is illustrated in which the cooperation of
ARQ and hybrid ARQ is provided. The physical layer (layer 1)
employs hybrid ARQ for retransmission control on a per-link basis.
As such, an individual hybrid ARQ retransmission process is
provided between the base station 14 and the relay station RS2;
between the relay station RS2 and the relay station RS1; and
between the relay station RS1 and the mobile station 16. Above the
physical layer resides a MAC layer in which ARQ retransmission
control is provided. Notably, ARQ retransmission techniques may be
provided between the base station 14 and the mobile station 16 at
the MAC layer. Within the MAC layer, an R-MAC layer is provided for
the base station 14, relay station RS2, and relay station RS1. The
relay station RS1 may also employ a MAC-lite layer to facilitate an
ARQ process with the mobile station 16. The R-MAC layers of the
base station 14, relay station RS2, and relay station RS1 may be
employed to provide ARQ processes between the base station 14 and
the relay station RS2, as well as between relay station RS2 and
relay station RS1, depending on the configuration of the
embodiment.
[0065] In one embodiment, the last relay station 18, which is the
one communicating directly with the mobile station 16, will keep
track of the service data unit sequence numbers (SDU_SN) associated
with each packet data unit (PDU) or PDU_SN, or the like, that is
received. When the mobile station 16 realizes that a PDU is lost or
corrupted, the mobile station 16 will send a negative
acknowledgement message to the base station 14. After the base
station 14 receives the ARQ or the negative acknowledgement, the
base station 14 may send a retransmission request identifying the
SDU_SNs associated with the PDUs to be retransmitted to the last
relay station 18, and perhaps scheduling information for
retransmitting the PDUs. The last relay station 18 will send a
retransmission response indicating whether or not the PDUs to be
retransmitted are still available at the last relay station 18. If
the PDUs are available at the last relay station 18, the last relay
station 18 will retransmit those PDUs to the mobile station 16.
Otherwise, the base station 14 will retransmit the PDUs to be
retransmitted directly or indirectly to the last relay station 18,
which will then retransmit the PDUs to the mobile station 16. The
messages exchanged between the base station 14 and the last relay
station 18 may identify the communication or call using a
communication ID (CID) as well as the SDU_SNs for the PDUs that
need to be retransmitted. Further, the last relay station 18 may
identify the SDU_SNs for both the available and the unavailable
PDUs at the last relay station 18.
[0066] With reference to FIGS. 14A and 14B, an exemplary
communication flow is provided to illustrate cooperation of ARQ and
hybrid ARQ according to one embodiment. Initially, assume PDU P1 is
transmitted from the base station 14 to relay station RS2 in an
effort to deliver the PDU P1 to the mobile station 16 (step 800).
Assume that the relay station RS2 did not receive the PDU P1, and
using a hybrid ARQ retransmission technique, determined that the
PDU P1 was lost or not properly detected, as indicated by the X. In
response, the relay station RS2 will send a hybrid negative
acknowledgement message (H-NACK) back to the base station 14 via
the physical layer (step 802). In response, the base station 14
will retransmit PDU P1 (step 804). Assuming that the relay station
RS2 properly received PDU P1, a hybrid acknowledgement message
(H-ACK) is transmitted to the base station 14 via the physical
layer (step 806). Assuming that relay station RS1 is the last relay
station in the downlink path, relay station RS2 will forward the
PDU P1 to the relay station RS1 (step 808). If RS1 properly
receives the PDU P1, an H-ACK is sent back to relay station RS2 at
the physical layer (step 810).
[0067] At this point, the relay station RS1 has received PDU P1,
and will attempt to transmit the PDU P1 to the mobile station 16
(step 812). Assume that the PDU P1 was not properly received. The
mobile station 16 is able to determine that the PDU P1 was not
properly received, and sends an H-NACK back to the relay station
RS1 via the physical layer to indicate that the PDU P1 was not
properly received (step 814). The relay station RS1 may attempt to
retransmit the PDU P1 automatically in response to receiving the
H-NACK (step 816). Further assume that the PDU P1 is not received
during retransmission, and as such the mobile station 16 provides
another H-NACK back to the relay station RS1 via the physical layer
(step 818).
[0068] During this time, assume that the base station 14 attempts
to send a second PDU P2 to relay station RS2 for ultimate delivery
to the mobile station 16 (step 820). If the PDU P2 is properly
received, the relay station RS2 will send an H-ACK back to the base
station 14 via the physical layer (step 822). The relay station RS2
will then forward the PDU P2 to the relay station RS1 (step 824),
wherein if the PDU P2 is properly received, an H-ACK is sent back
to the relay station RS2 via the physical layer (step 826). Next,
the relay station RS1 will attempt to transmit the PDU P2 to the
mobile station 16 (step 828). Assuming that the PDU P2 is properly
received by the mobile station 16, an H-ACK is sent back to the
relay station RS1 via the physical layer (step 830).
[0069] At this point, the mobile station 16 may look at the SDU_SN
of the PDU P2 and recognize that PDU P1 was not received. As such,
the mobile station 16 may send a negative acknowledgement message
(NACK) indicating that PDU P1 was not received via the MAC layer
(step 832). The NACK may include the sequence numbers for the PDUs
that were not received, including PDU P1. The base station 14 will
respond by sending a retransmission request to the relay station
RS1 directly or via relay station RS2 (step 834). The
retransmission request will include the communication IDs as well
as the sequence numbers for the PDUs to be retransmitted. The relay
station RS1 will acknowledge receipt of the retransmission request
and identify the sequence numbers for the PDUs it has available for
retransmission in a retransmission response, which is sent back to
the base station 14 (step 836).
[0070] At this point, the relay station RS1 will attempt to
retransmit the PDU P1, which has been stored since its receipt from
the relay station RS2 (at step 808) to the mobile station 16 (step
838). If the PDU P1 is not properly received, the mobile station 16
may detect this and send an H-NACK back to the relay station RS1
via the physical layer (step 840). The relay station RS1 may
attempt to retransmit the PDU P1 (step 842). Upon proper receipt,
the mobile station 16 may send an H-ACK back to the relay station
RS1 (step 844).
[0071] In yet another embodiment, the last relay station 18 may
identify a lost PDU in response to receiving an H-NACK from the
mobile station 16. In response, the last relay station 18 may send
a retransmission report that identifies the lost PDUs to the base
station 14. In response, the base station 14 may send a
retransmission request to the last relay station 18, which will
retransmit the lost PDUs. Notably, the base station 14 may ignore
any subsequent ACK or NACK messages that are provided at the MAC
layer. In this embodiment, authorization to retransmit lost PDUs is
quickly provided to the last relay station 18. An overview of this
embodiment is provided in the communication flow of FIGS. 15A and
15B.
[0072] Initially, assume PDU P1 is transmitted from the base
station 14 to relay station RS2 in an effort to deliver the PDU P1
to the mobile station 16 (step 900). Assume that the relay station
RS2 did not receive the PDU P1, and using a hybrid ARQ
retransmission technique, determined that the PDU P1 was lost or
not properly detected, as indicated by the X. In response, the
relay station RS2 will send a hybrid negative acknowledgement
message (H-NACK) back to the base station 14 via the physical layer
(step 902). In response, the base station 14 will retransmit PDU P1
(step 904). Assuming that the relay station RS2 properly received
PDU P1, a hybrid acknowledgement message (H-ACK) is transmitted to
the base station 14 via the physical layer (step 906). Assuming
that relay station RS1 is the last relay station in the downlink
path, relay station RS2 will forward the PDU P1 to the relay
station RS1 (step 908). If RS1 properly receives the PDU P1, an
H-ACK is sent back to relay station RS2 at the physical layer (step
910).
[0073] At this point, the relay station RS1 has received PDU P1,
and will attempt to transmit the PDU P1 to the mobile station 16
(step 912). Assume that the PDU P1 was not properly received. The
mobile station 16 is able to determine that the PDU P1 was not
properly received, and sends a H-NACK back to the relay station RS1
via the physical layer to indicate that the PDU P1 was not properly
received (step 914). The relay station RS1 may attempt to
retransmit the PDU P1 automatically in response to receiving the
H-NACK (step 916). Further assume that the PDU P1 is not received
during retransmission, and as such the mobile station 16 provides
another H-NACK back to the relay station RS1 via the physical layer
(step 918). At this point, the relay station RS1, through the
H-NACK, will recognize that PDU P1 was not properly received by the
mobile station 16. In response, the relay station RS1 will send a
retransmission report directly or indirectly to the base station 14
(step 920). The retransmission report may identify PDU P1 directly
or through a sequence number and the associated communication ID.
The base station 14 may process the retransmission report and send
a retransmission request to instruct the relay station RS1 to
retransmit PDU P1 to the mobile station 16 (step 922). The
retransmission request may identify the sequence numbers for the
PDUs to be retransmitted along with the communication IDs. Notably,
these messages may identify PDUs for the same or different
communication IDs, and may include one or more sequence numbers for
any number of PDUs. The relay station RS1 may respond by sending a
retransmission response back to the base station 14 indicating that
the retransmission request was received, and confirming the PDUs to
be retransmitted for the corresponding communication IDs (step
924).
[0074] During this time, assume that the base station 14 attempts
to send a second PDU P2 to relay station RS2 for ultimate delivery
to the mobile station 16 (step 926). If the PDU P2 is properly
received, the relay station RS2 will send an H-ACK back to the base
station 14 via the physical layer (step 928). The relay station RS2
will then forward the PDU P2 to the relay station RS1 (step 930),
wherein if the PDU P2 is properly received, an H-ACK is sent back
to the relay station RS2 via the physical layer (step 932). Next,
the relay station RS1 will attempt to transmit the PDU P2 to the
mobile station 16 (step 934). Assuming that the PDU P2 is properly
received by the mobile station 16, an H-ACK is sent back to the
relay station RS1 via the physical layer (step 936).
[0075] At this point, the mobile station 16 may look at the SDU_SN
of the PDU P2 and recognize that PDU P1 was not received. As such,
the mobile station 16 may send a negative acknowledgement message
(NACK) indicating that PDU P1 was not received via the MAC layer
(step 938). Since the base station 14 has already recognized that
PDU P1 was not properly received and has already sent a request
instructing relay station RS1 to retransmit PDU P1 to the mobile
station 16, the NACK that was received via the MAC layer may be
ignored.
[0076] In response to the retransmission request, the relay station
RS1 will then attempt to retransmit the PDU P1 to the mobile
station 16 (step 940). If the PDU P1 is not properly received, the
mobile station 16 may detect this and send an H-NACK back to the
relay station RS1 via the physical layer (step 942). The relay
station RS1 may attempt to retransmit the PDU P1 (step 944). Upon
proper receipt, the mobile station 16 may send an H-ACK back to the
relay station RS1 (step 946).
[0077] A high level overview of the mobile stations 16 and base
stations 14 of the present invention is provided in following
discussion. With reference to FIG. 16, a base station 14 configured
according to one embodiment of the present invention is
illustrated. The base station 14 generally includes a control
system 20, a baseband processor 22, transmit circuitry 24, receive
circuitry 26, one or more antennas 28, and a network interface 30.
The receive circuitry 26 receives radio frequency signals bearing
information from one or more remote transmitters provided by mobile
stations 16 or relay stations 18. Preferably, a low noise amplifier
and a filter (not shown) cooperate to amplify and remove broadband
interference from the signal for processing. Downconversion and
digitization circuitry (not shown) will then downconvert the
filtered, received signal to an intermediate or baseband frequency
signal, which is then digitized into one or more digital
streams.
[0078] The baseband processor 22 processes the digitized received
signal to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations. As such, the baseband
processor 22 is generally implemented in one or more digital signal
processors (DSPs). The received information is then sent across a
wireless network via the network interface 30 or transmitted to
another mobile station 16 or relay station 18 serviced by the base
station 14. The network interface 30 will typically interact with a
base station controller and a circuit-switched network forming a
part of the access network, which may be coupled to the public
switched telephone network (PSTN) to form the carrier network
12.
[0079] On the transmit side, the baseband processor 22 receives
digitized data, which may represent voice, data, or control
information, from the network interface 30 under the control of
control system 20, which encodes the data for transmission. The
encoded data is output to the transmit circuitry 24, where it is
modulated by a carrier signal having a desired transmit frequency
or frequencies. A power amplifier (not shown) will amplify the
modulated carrier signal to a level appropriate for transmission,
and deliver the modulated carrier signal to the antennas 28 through
a matching network (not shown). Modulation and processing details
are described in greater detail below.
[0080] In order to allow the relay station 18 or mobile station 16
to request bandwidth or additional bandwidth, quality of service
information must be provided along with the request. Quality of
service information may include priority, service class, scheduling
information, or the like.
[0081] With reference to FIG. 17, a mobile station 16 configured
according to one embodiment of the present invention is
illustrated. Similarly to the base station 14, the mobile station
16 will include a control system 32, a baseband processor 34,
transmit circuitry 36, receive circuitry 38, one or more antennas
40, and user interface circuitry 42. The receive circuitry 38
receives radio frequency signals bearing information from one or
more base stations 14 or relay stations 18. Preferably, a low noise
amplifier and a filter (not shown) cooperate to amplify and remove
broadband interference from the signal for processing.
Downconversion and digitization circuitry (not shown) will then
downconvert the filtered, received signal to an intermediate or
baseband frequency signal, which is then digitized into one or more
digital streams.
[0082] The baseband processor 34 processes the digitized received
signal to extract the information or data bits conveyed in the
received signal. This processing typically comprises demodulation,
decoding, and error correction operations, as will be discussed on
greater detail below. The baseband processor 34 is generally
implemented in one or more digital signal processors (DSPs) and
application specific integrated circuits (ASICs).
[0083] For transmission, the baseband processor 34 receives
digitized data, which may represent voice, data, or control
information, from the control system 32, which it encodes for
transmission. The encoded data is output to the transmit circuitry
36, where it is used by a modulator to modulate a carrier signal
that is at a desired transmit frequency or frequencies. A power
amplifier (not shown) will amplify the modulated carrier signal to
a level appropriate for transmission, and deliver the modulated
carrier signal to the antennas 40 through a matching network (not
shown). Various modulation and processing techniques available to
those skilled in the art are applicable to the present
invention.
[0084] In OFDM modulation, the transmission band is divided into
multiple, orthogonal carrier waves. Each carrier wave is modulated
according to the digital data to be transmitted. Because OFDM
divides the transmission band into multiple carriers, the bandwidth
per carrier decreases and the modulation time per carrier
increases. Since the multiple carriers are transmitted in parallel,
the transmission rate for the digital data, or symbols, on any
given carrier is lower than when a single carrier is used.
[0085] OFDM modulation generally employs an Inverse Fast Fourier
Transform (IFFT) on the information to be transmitted. For
demodulation, the performance of a Fast Fourier Transform (FFT) on
the received signal is required to recover the transmitted
information. In practice, the Inverse Discrete Fourier Transform
(IDFT) and Discrete Fourier Transform (DFT) are implemented using
digital signal processing for modulation and demodulation,
respectively.
[0086] Accordingly, the characterizing feature of OFDM modulation
is that orthogonal carrier waves are generated for multiple bands
within a transmission channel. The modulated signals are digital
signals having a relatively low transmission rate and capable of
staying within their respective bands. The individual carrier waves
are not modulated directly by the digital signals. Instead, all
carrier waves are modulated at once by IFFT processing.
[0087] In the preferred embodiment, OFDM is used at least for the
downlink transmission from the base stations 14 or relay stations
18 to the mobile stations 16. Further, the base stations 14 are
synchronized to a common clock via GPS signaling and coordinate
communications via a base station controller. Each base station 14
may be equipped with n transmit antennas 28, and each mobile
station 16 is equipped with m receive antennas 40. Notably, the
respective antennas can be used for reception and transmission
using appropriate duplexers or switches and are so labeled only for
clarity. Notably, the present invention is equally application to
single antenna embodiments at the mobile station 16, relay stations
18, and the base stations 14.
[0088] With reference to FIG. 18, a relay station 18 configured
according to one embodiment of the present invention is
illustrated. Notably, the basic architecture of a relay station 18
is very analogous to a mobile station 16 with the exception that
the relay station 18 is able to communicate wirelessly with base
stations 14 as well as mobile stations 16. Accordingly, the relay
station 18 will include a control system 32', a baseband processor
34', transmit circuitry 36', receive circuitry 38', one or more
antennas 40', and user interface circuitry 42'. The receive
circuitry 38' receives radio frequency signals bearing information
from one or more base stations 14 or mobile stations 18 and the
transmit circuitry 36' transmits radio frequency signals to one or
more base stations or mobile stations. The baseband processor 34'
and control system 32' operate in a fashion similar to the
corresponding elements of the mobile station 16 and the base
station 14.
[0089] With reference to FIG. 19, a logical OFDM transmission
architecture of a mobile station 16, base station 14, or relay
station 18 is provided according to one embodiment. For clarity and
conciseness, assume the following transmission architecture is in a
base station 14. The data 44 to be transmitted is a stream of bits,
which is scrambled in a manner reducing the peak-to-average power
ratio associated with the data using data scrambling logic 46. A
cyclic redundancy check (CRC) for the scrambled data is determined
and appended to the scrambled data using CRC logic 48. Next,
channel coding is performed using channel encoder logic 50 to
effectively add redundancy to the data to facilitate recovery and
error correction at the mobile station 16. The channel encoder
logic 50 uses known Turbo encoding techniques in one embodiment.
The encoded data is then processed by rate matching logic 52 to
compensate for the data expansion associated with encoding.
[0090] Bit interleaver logic 54 systematically reorders the bits in
the encoded data to minimize the loss of consecutive data bits. The
resultant data bits are systematically mapped into corresponding
symbols depending on the chosen baseband modulation by mapping
logic 56. Preferably, Quadrature Amplitude Modulation (QAM) or
Quadrature Phase Shift Key (QPSK) modulation is used. The symbols
may be systematically reordered to further bolster the immunity of
the transmitted signal to periodic data loss caused by frequency
selective fading using symbol interleaver logic 58.
[0091] At this point, groups of bits have been mapped into symbols
representing locations in an amplitude and phase constellation.
Blocks of symbols are then processed by space-time block code (STC)
encoder logic 60, which modifies the symbols in a fashion making
the transmitted signals more resistant to interference and more
readily decoded at a mobile station 16. The STC encoder logic 60
will process the incoming symbols and provide n outputs
corresponding to the number of transmit antennas 28 for the base
station 14. The control system 20 and/or baseband processor 22 will
provide a mapping control signal to control STC encoding. At this
point, assume the symbols for the n outputs are representative of
the data to be transmitted and capable of being recovered by the
mobile station 16. See A. F. Naguib, N. Seshadri, and A. R.
Calderbank, "Applications of space-time codes and interference
suppression for high capacity and high data rate wireless systems,"
Thirty-Second Asilomar Conference on Signals, Systems &
Computers, Volume 2, pp. 1803-1810, 1998, which is incorporated
herein by reference in its entirety.
[0092] For the present example, assume the base station 14 has two
antennas 28 (n=2) and the STC encoder logic 60 provides two output
streams of symbols. Accordingly, each of the symbol streams output
by the STC encoder logic 60 is sent to a corresponding IFFT
processor 62, illustrated separately for ease of understanding.
Those skilled in the art will recognize that one or more processors
may be used to provide such digital signal processing alone or in
combination with other processing described herein. The IFFT
processors 62 will preferably operate on the respective symbols
using IDFT or like processing to effect an inverse Fourier
Transform. The output of the IFFT processors 62 provides symbols in
the time domain. The time domain symbols are grouped into frames,
which are associated with prefix and pilot headers by like
insertion logic 64. Each of the resultant signals is up-converted
in the digital domain to an intermediate frequency and converted to
an analog signal via the corresponding digital up-conversion (DUC)
and digital-to-analog (D/A) conversion circuitry 66. The resultant
(analog) signals are then simultaneously modulated at the desired
RF frequency, amplified, and transmitted to via the RF circuitry 68
and antennas 28. Notably, the transmitted data is preceded by pilot
signals, which are known by the intended mobile station 16 and
implemented by modulating the pilot header and scattered pilot
sub-carriers. The mobile station 16 may use the scattered pilot
signals for channel estimation and interference suppression and the
header for identification of the base station 14. Again, this
architecture may be provided in relay stations 18 and mobile
stations 16.
[0093] Reference is now made to FIG. 20 to illustrate reception of
the transmitted signals by a mobile station 16; however, the
principles may be applied to a base station 14 or relay station 18
Upon arrival of the transmitted signals at each of the antennas 40
of the mobile station 16, the respective signals are demodulated
and amplified by corresponding RF circuitry 70. For the sake of
conciseness and clarity, only one of the two receive paths is
described and illustrated in detail. Analog-to-digital (A/D)
converter and down-conversion circuitry 72 digitizes and
downconverts the analog signal for digital processing. The
resultant digitized signal may be used by automatic gain control
circuitry (AGC) 74 to control the gain of the amplifiers in the RF
circuitry 70 based on the received signal level.
[0094] Preferably, each transmitted frame has a defined structure
having two identical headers. Framing acquisition is based on the
repetition of these identical headers. Initially, the digitized
signal is provided to synchronization logic 76, which includes
coarse synchronization logic 78, which buffers several OFDM symbols
and calculates an auto-correlation between the two successive OFDM
symbols. A resultant time index corresponding to the maximum of the
correlation result determines a fine synchronization search window,
which is used by the fine synchronization logic 80 to determine a
precise framing starting position based on the headers. The output
of the fine synchronization logic 80 facilitates frame acquisition
by the frame alignment logic 84. Proper framing alignment is
important so that subsequent FFT processing provides an accurate
conversion from the time to the frequency domain. The fine
synchronization algorithm is based on the correlation between the
received pilot signals carried by the headers and a local copy of
the known pilot data. Once frame alignment acquisition occurs, the
prefix of the OFDM symbol is removed with prefix removal logic 86
and a resultant samples are sent to frequency offset and Doppler
correction logic 88, which compensates for the system frequency
offset caused by the unmatched local oscillators in the transmitter
and the receiver and Doppler effects imposed on the transmitted
signals. Preferably, the synchronization logic 76 includes
frequency offset, Doppler, and clock estimation logic 82, which is
based on the headers to help estimate such effects on the
transmitted signal and provide those estimations to the correction
logic 88 to properly process OFDM symbols.
[0095] At this point, the OFDM symbols in the time domain are ready
for conversion to the frequency domain using the FFT processing
logic 90. The results are frequency domain symbols, which are sent
to processing logic 92. The processing logic 92 extracts the
scattered pilot signal using scattered pilot extraction logic 94,
determines a channel estimate based on the extracted pilot signal
using channel estimation logic 96, and provides channel responses
for all sub-carriers using channel reconstruction logic 98. The
frequency domain symbols and channel reconstruction information for
each receive path are provided to an STC decoder 100, which
provides STC decoding on both received paths to recover the
transmitted symbols. The channel reconstruction information
provides the STC decoder 100 sufficient information to process the
respective frequency domain symbols to remove the effects of the
transmission channel.
[0096] The recovered symbols are placed back in order using the
symbol de-interleaver logic 102, which corresponds to the symbol
interleaver logic 58 of the transmitter. The de-interleaved symbols
are then demodulated or de-mapped to a corresponding bitstream
using de-mapping logic 104. The bits are then de-interleaved using
bit de-interleaver logic 106, which corresponds to the bit
interleaver logic 54 of the transmitter architecture. The
de-interleaved bits are then processed by rate de-matching logic
108 and presented to channel decoder logic 110 to recover the
initially scrambled data and the CRC checksum. Accordingly, CRC
logic 112 removes the CRC checksum, checks the scrambled data in
traditional fashion, and provides it to the de-scrambling logic 114
for de-scrambling using the known base station de-scrambling code
to recover the originally transmitted data.
[0097] While certain embodiments are discussed in the context of
wireless networks operating in accordance with the IEEE 802.16
broadband wireless standard, which is hereby incorporated by
reference, the invention is not limited in this regard and may be
applicable to other broadband networks including those operating in
accordance with other OFDM-based systems including the 3rd
Generation Partnership Project ("3GPP") and 3GPP2 evolutions.
Similarly, the present invention is not limited solely to
OFDM-based systems and can be implemented in accordance with other
system technologies, such as code division multiple access
technologies or other frequency division multiple access
technologies.
[0098] Those skilled in the art will recognize improvements and
modifications to the preferred embodiments of the present
invention. All such improvements and modifications are considered
within the scope of the concepts disclosed herein and the claims
that follow.
* * * * *